import java.util.Scanner;
class Point{
double x;	
double y;	
Point(double x,double y){
this.x=x;
this.y=y;
}
public double distance(Point a){
return Math.abs(Math.sqrt(Math.pow((this.x-a.x),2)+Math.pow((this.y-a.y),2)));
}
}
public class Main{
public static void main(String[] args){
Scanner read=new Scanner(System.in

);
String readLine=read.nextLine();	
String[] data=readLine.split(" ");	
Point pointA=new Point(Integer.valueOf(data[0]),Integer.valueOf(data[1]));	
readLine=read.nextLine();
data=readLine.split(" ");	
Point pointB=new Point(Integer.valueOf(data[0]),Integer.valueOf(data[1]));	
System.out.printf("%.2f",pointA.distance(pointB));	
}
}

 
